26. What are modules?

In JavaScript, modules are reusable pieces of code that can be imported and exported between files. They help in organizing code by breaking it into smaller, manageable parts, promoting reusability and maintainability.

Example of JavaScript Modules

JavaScript uses ES6 Modules (ECMAScript 2015), where we use the export and import keywords.

1. Creating a Module (Exporting)

Let's create a file named math.js that contains functions for addition and subtraction:

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// math.js
export function add(a, b) {
    return a + b;
}

export function subtract(a, b) {
    return a - b;
}

2. Importing the Module in Another File

Now, in another file app.js, we can import and use these functions:

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// app.js
import { add, subtract } from './math.js';

console.log(add(5, 3));      // Output: 8
console.log(subtract(10, 4)); // Output: 6

Using Default Export

A module can have a default export, which allows importing without curly braces {}.

Example of Default Export

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// greet.js
export default function greet(name) {
    return `Hello, ${name}!`;
}

Importing a Default Export

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// app.js
import greet from './greet.js';

console.log(greet('Alice')); // Output: Hello, Alice!

Why Use Modules?

1. Code Reusability – Write once, use everywhere.
2. Encapsulation – Prevents polluting the global scope.
3. Maintainability – Easier to manage and debug.
4. Lazy Loading – Load modules only when needed.

Would you like more advanced examples, like dynamic imports or CommonJS modules? 🚀